0 00:00:16,549 --> 00:00:18,824 Of all our planet's forces, 1 00:00:18,869 --> 00:00:23,465 perhaps none has greater power over us than water. 2 00:00:26,749 --> 00:00:31,265 For me, water's the most magical force on Earth. 3 00:00:32,709 --> 00:00:36,145 The presence of water shapes, renews and nourishes our planet. 4 00:00:36,189 --> 00:00:38,862 Oh, my gosh! You're getting all wet there! 5 00:00:43,589 --> 00:00:45,580 It's our planet's lifeblood. 6 00:00:45,629 --> 00:00:47,824 It pumps through it continuously, 7 00:00:47,869 --> 00:00:49,780 delivering vital ingredients for life. 8 00:00:49,829 --> 00:00:51,785 Ah, it's glorious. 9 00:01:02,189 --> 00:01:05,306 Water makes Earth alive. 10 00:01:08,429 --> 00:01:10,943 Yet water is just one of the ways 11 00:01:10,989 --> 00:01:14,868 that the power of the planet has shaped our lives. 12 00:01:16,869 --> 00:01:19,258 The Earth has immense power... 13 00:01:23,109 --> 00:01:27,068 ...and yet that's rarely mentioned in our history books. 14 00:01:28,229 --> 00:01:30,663 I'm here to change that. 15 00:01:32,909 --> 00:01:37,824 In this series, I'm exploring four great planetary forces 16 00:01:37,869 --> 00:01:40,383 that have influenced our history. 17 00:01:45,229 --> 00:01:47,106 The power of the deep Earth... 18 00:01:50,429 --> 00:01:52,385 ...that fuelled technological innovation. 19 00:01:54,469 --> 00:01:55,982 Wind. 20 00:01:56,029 --> 00:01:59,180 It has shaped the fate of entire continents. 21 00:01:59,229 --> 00:02:01,538 And fire... 22 00:02:03,989 --> 00:02:07,504 ...which gave us the power to conquer the planet. 23 00:02:08,869 --> 00:02:11,861 But I'm going to start with water. 24 00:02:12,909 --> 00:02:17,061 The magic of water is that it's constantly transforming itself, 25 00:02:17,109 --> 00:02:21,978 shifting between guises and from place to place. 26 00:02:22,029 --> 00:02:27,262 Our struggle to control it has been behind the rise and fall 27 00:02:27,309 --> 00:02:30,381 of some of the greatest civilisations on Earth. 28 00:02:56,189 --> 00:02:59,704 The centre of the Sahara Desert in North Africa. 29 00:03:01,669 --> 00:03:04,263 One of the driest places on Earth. 30 00:03:09,589 --> 00:03:13,184 I'm over six hours'drive from civilisation. 31 00:03:15,749 --> 00:03:20,220 Temperatures here regularly reach 4o degrees Celsius, 32 00:03:20,269 --> 00:03:23,579 and there's less than a centimetre of rainfall each year. 33 00:03:25,269 --> 00:03:26,748 Ah.... 34 00:03:29,869 --> 00:03:31,348 The whole thing's moving. 35 00:03:32,509 --> 00:03:33,737 (HE STRAINS) 36 00:03:34,749 --> 00:03:37,183 It's like walking on water. 37 00:03:38,509 --> 00:03:41,626 Yet hidden amongst these dry dunes are clues 38 00:03:41,669 --> 00:03:47,107 that point to the dramatic influence the planet has had on human lives. 39 00:03:54,349 --> 00:03:57,546 I've come here because although you'd never know it, 40 00:03:57,589 --> 00:04:01,264 the story of this place is all about water. 41 00:04:01,309 --> 00:04:05,746 The clues are etched into that rock face there. 42 00:04:05,789 --> 00:04:10,021 Prehistoric rock art dating back 6,OOO years, 43 00:04:10,069 --> 00:04:13,823 and depicting the most unlikely cast of characters you've ever seen. 44 00:04:17,029 --> 00:04:19,702 Wow, what is that? 45 00:04:19,749 --> 00:04:21,580 It's a giraffe... 46 00:04:21,629 --> 00:04:24,382 It's a giraffe, look at it, there's the neck. 47 00:04:24,429 --> 00:04:26,579 There's its ears, that's an eye, 48 00:04:26,629 --> 00:04:28,745 and its mouth. 49 00:04:28,789 --> 00:04:30,347 That's really natural, isn't it? 50 00:04:30,389 --> 00:04:32,949 And this looks like the giraffe dipping its head down, 51 00:04:32,989 --> 00:04:36,186 drinking some water - we've got a herd of giraffes here! 52 00:04:44,789 --> 00:04:47,178 There's two cats. 53 00:04:47,229 --> 00:04:49,299 They're fighting. 54 00:04:53,429 --> 00:04:55,738 This... What is this? 55 00:04:55,789 --> 00:04:59,828 It looks like the figure of a man, but he's wearing a bikini. 56 00:05:05,509 --> 00:05:09,343 And this is clearly a crocodile, which is especially odd here. 57 00:05:09,389 --> 00:05:12,506 This is an aquatic animal, it doesn't just paddle around. 58 00:05:12,549 --> 00:05:15,541 It needs a lot of water to live in. In fact, 59 00:05:15,589 --> 00:05:18,979 all the creatures that are depicted on these rocks are not desert animals - 60 00:05:19,029 --> 00:05:21,418 they need wet conditions. 61 00:05:25,589 --> 00:05:29,264 In such a parched wilderness, how can this be? 62 00:05:32,269 --> 00:05:37,707 The only explanation is that 6,ooo years ago, this place was wet. 63 00:05:44,429 --> 00:05:49,059 Once you know what to look for, the evidence is all around. 64 00:05:51,549 --> 00:05:55,144 Up there is a river valley that's been carved out into the rock, 65 00:05:55,189 --> 00:05:57,464 and it's been carved by running water 66 00:05:57,509 --> 00:06:01,297 which has flowed down here, smoothing off this rock bed, 67 00:06:01,349 --> 00:06:04,227 and then cascaded down into the valley and off there. 68 00:06:04,269 --> 00:06:08,057 6,OOO years ago, that was a big river. 69 00:06:23,189 --> 00:06:27,307 Satellite images reveal that the river bed I'm standing in 70 00:06:27,349 --> 00:06:30,705 is just one of a network of past river valleys 71 00:06:30,749 --> 00:06:33,024 that crisscross the Sahara Desert. 72 00:06:38,669 --> 00:06:44,539 1 o,ooo years ago, this dry, empty place was entirely different. 73 00:06:47,749 --> 00:06:51,139 Little is known about the early Saharans who lived here then, 74 00:06:51,189 --> 00:06:55,467 but we do know that they depended entirely on water. 75 00:06:58,629 --> 00:07:01,427 Water formed the lakes in which they swam. 76 00:07:02,629 --> 00:07:06,338 Water nourished the plants which fed the animals they hunted. 77 00:07:09,749 --> 00:07:13,219 Water filled the clay pots from which they drank. 78 00:07:18,709 --> 00:07:21,507 But then the climate changed. 79 00:07:21,549 --> 00:07:26,942 About 5,5OO years ago, the Sahara began to dry. 80 00:07:26,989 --> 00:07:31,665 The rains failed, the rivers shrank, and the lakes dried out. 81 00:07:32,829 --> 00:07:35,821 For the early Saharan people there was only one option - 82 00:07:35,869 --> 00:07:40,260 to follow the rains and abandon the desert. 83 00:07:44,589 --> 00:07:47,865 The fortunes of the early Saharan people 84 00:07:47,909 --> 00:07:50,059 reveal a universal, timeless truth - 85 00:07:50,109 --> 00:07:53,624 our fate is inextricably linked to water. 86 00:07:53,669 --> 00:07:57,457 The problem is, water never stands still. 87 00:07:57,509 --> 00:08:00,581 It's always on the move across the planet. 88 00:08:05,189 --> 00:08:07,578 We think of this as a blue planet. 89 00:08:07,629 --> 00:08:12,020 But while water is abundant, most of it is no use. 90 00:08:13,869 --> 00:08:19,262 More than 97% of the Earth's water is salty ocean, which we can't drink 91 00:08:19,309 --> 00:08:21,459 or use to grow crops. 92 00:08:24,949 --> 00:08:30,546 Less than 3% is fresh water, on which all human life hangs. 93 00:08:31,629 --> 00:08:35,827 What's more, that tiny fraction is often hard to pin down, 94 00:08:35,869 --> 00:08:40,385 because fresh water has a life cycle all of its own. 95 00:08:47,589 --> 00:08:53,744 I'm about to explore that cycle, in all its elusive glory. 96 00:08:58,109 --> 00:09:00,942 You know, water seems so familiar, doesn't it? 97 00:09:00,989 --> 00:09:03,457 But to see its remarkable qualities 98 00:09:03,509 --> 00:09:05,659 you have to go to some extreme lengths. 99 00:09:07,109 --> 00:09:09,987 (MOTOR CHUGS INTO LIFE) 100 00:09:10,029 --> 00:09:13,624 (REWING) 101 00:09:16,789 --> 00:09:18,700 Here we go... 102 00:09:18,749 --> 00:09:21,309 Ho-ho! Feel that! 103 00:09:21,349 --> 00:09:23,180 ( # WAGNER: Ride Of The Valkyries) 104 00:09:23,229 --> 00:09:25,265 Here we go! 105 00:09:25,309 --> 00:09:28,779 Oh... Hey-hey! Oh, we're off! 106 00:09:28,829 --> 00:09:30,740 Oh, my God! 107 00:09:30,789 --> 00:09:32,620 It's a bit bouncy! 108 00:09:34,749 --> 00:09:37,627 I shouldn't have had that bacon and eggs this morning. 109 00:09:43,149 --> 00:09:45,902 O-o-o-h! (LAUGHS) 110 00:09:48,469 --> 00:09:53,702 The fresh water that we depend on begins its life in the oceans. 111 00:09:56,389 --> 00:10:00,746 As the sun's rays beat down on the surface of the sea, 112 00:10:00,789 --> 00:10:04,304 they heat the water molecules until some evaporate. 113 00:10:05,429 --> 00:10:09,547 It's the start of an extraordinary journey. 114 00:10:09,589 --> 00:10:12,820 You know, when water evaporates, 115 00:10:12,869 --> 00:10:15,702 it feels as if it vanishes into thin air. 116 00:10:15,749 --> 00:10:17,865 But although we barely notice it, 117 00:10:17,909 --> 00:10:21,948 water molecules are suspended around us all the time. 118 00:10:24,189 --> 00:10:27,101 It's just that we're only aware of it when they clump together 119 00:10:27,149 --> 00:10:29,299 as cloud. 120 00:10:34,149 --> 00:10:40,258 At any one time, less than a thousandth of the world's fresh water is up here 121 00:10:40,309 --> 00:10:42,664 in the atmosphere. 122 00:10:42,709 --> 00:10:47,863 It may not seem much, but this is what spreads water from the seas to the land. 123 00:10:50,349 --> 00:10:54,740 A water molecule doesn't hang around up here for very long. 124 00:10:54,789 --> 00:10:57,781 In fact, it spends less time up here in the atmosphere 125 00:10:57,829 --> 00:10:59,865 than at any other time on its journey - 126 00:10:59,909 --> 00:11:01,706 a mere nine days 127 00:11:01,749 --> 00:11:06,823 until the typical water molecule crashes to Earth as rain. 128 00:11:08,989 --> 00:11:11,549 (THUNDER RUMBLES) 129 00:11:11,589 --> 00:11:13,500 (BIRD SQUAWKS) 130 00:11:16,109 --> 00:11:18,304 For most of us, rain is perhaps 131 00:11:18,349 --> 00:11:20,988 the most familiar stage of the water cycle, 132 00:11:21,029 --> 00:11:24,226 but notoriously the least reliable. 133 00:11:25,509 --> 00:11:28,899 As the water falls as rain, it joins a bigger system, 134 00:11:28,949 --> 00:11:34,899 cascading and carving its way across the land surface as streams and rivers. 135 00:11:39,629 --> 00:11:41,301 Look at that! 136 00:11:41,349 --> 00:11:43,419 Water absolutely everywhere! 137 00:11:45,509 --> 00:11:49,184 Rivers and rain are the part of the water cycle that we depend on. 138 00:11:50,749 --> 00:11:53,582 Whoo-hoo! 139 00:11:53,629 --> 00:11:58,100 And yet they're only a tiny proportion of the world's fresh water... 140 00:11:59,669 --> 00:12:04,379 ...a measly 2% of all fresh water on the planet. 141 00:12:04,429 --> 00:12:07,023 The rest of the Earth's fresh water 142 00:12:07,069 --> 00:12:10,266 is locked away down there, on the ground. 143 00:12:10,309 --> 00:12:12,823 Oh... (LAUGHING) 144 00:12:12,869 --> 00:12:14,382 Oh! 145 00:12:14,429 --> 00:12:15,748 What a landing! 146 00:12:16,869 --> 00:12:20,305 The vast majority of it is stored as ice. 147 00:12:23,549 --> 00:12:26,347 Most of the rest seeps deep into the Earth, 148 00:12:26,389 --> 00:12:29,347 where it's known as groundwater. 149 00:12:30,909 --> 00:12:33,787 Hidden away down here 150 00:12:33,829 --> 00:12:36,946 is the planet's second-largest store of fresh water. 151 00:12:42,829 --> 00:12:46,868 But in the end, all water arrives back in the oceans, 152 00:12:46,909 --> 00:12:48,740 and the cycle begins again. 153 00:12:59,629 --> 00:13:01,699 What that circulation means for us humans 154 00:13:01,749 --> 00:13:05,298 is that water is a moving target. 155 00:13:05,349 --> 00:13:10,104 We constantly have to seek it out on its endless cycle and intercept it 156 00:13:10,149 --> 00:13:12,982 wherever and whenever we can. 157 00:13:13,029 --> 00:13:14,542 This quest to... 158 00:13:14,589 --> 00:13:20,346 to pin down water has played a defining role in human history. 159 00:13:23,829 --> 00:13:26,662 You can trace the impact of our quest for water 160 00:13:26,709 --> 00:13:30,179 right back to the dawn of civilisation, 161 00:13:30,229 --> 00:13:32,299 about 1 2,ooo years ago. 162 00:13:32,349 --> 00:13:35,102 It all began with a big block of ice. 163 00:13:37,789 --> 00:13:39,427 1 2,ooo years ago, 164 00:13:39,469 --> 00:13:44,497 much of the northern hemisphere was covered in a single, huge ice sheet. 165 00:13:49,989 --> 00:13:52,628 And even today you can see its legacy... 166 00:13:54,269 --> 00:13:56,863 ...here in Iceland. 167 00:14:01,349 --> 00:14:07,026 This glacier is a tiny remnant of that once enormous expanse of ice. 168 00:14:19,229 --> 00:14:24,747 Ice is like a storage cupboard in the circulation of water around the planet, 169 00:14:24,789 --> 00:14:29,067 a store into which water can be deposited or withdrawn. 170 00:14:31,989 --> 00:14:35,425 And it was a shift in the amount of water locked up here 171 00:14:35,469 --> 00:14:40,782 that was to drive one of the greatest ever transformations of human society. 172 00:14:43,629 --> 00:14:47,144 Today, the ice sheet here is melting and retreating, 173 00:14:47,189 --> 00:14:49,862 and releasing this great armada of icebergs. 174 00:14:49,909 --> 00:14:52,628 But if you go back 1 2,5OO years ago, 175 00:14:52,669 --> 00:14:55,627 it's a very different story. 176 00:14:55,669 --> 00:14:58,820 Then the ice was expanding, 177 00:14:58,869 --> 00:15:02,498 sucking moisture out of the atmosphere in vast quantities 178 00:15:02,549 --> 00:15:04,460 and locking it away in the ice. 179 00:15:04,509 --> 00:15:07,899 And the effects of that were felt right across the planet. 180 00:15:22,589 --> 00:15:25,103 Thousands of kilometres away in the Middle East... 181 00:15:27,749 --> 00:15:31,298 ...it led to a drought which lasted for centuries. 182 00:15:33,429 --> 00:15:37,138 It had its most profound impact in what would become known 183 00:15:37,189 --> 00:15:43,662 as the Fertile Crescent, an area famed for its exceptionally rich soil. 184 00:15:49,509 --> 00:15:53,343 This drought would trigger the start of the defining characteristic 185 00:15:53,389 --> 00:15:55,027 of human civilisation. 186 00:15:58,709 --> 00:16:02,463 Back then, every human on the planet was a hunter-gatherer. 187 00:16:02,509 --> 00:16:07,663 Those living in the Fertile Crescent, the Natufians, thrived on rich pickings 188 00:16:07,709 --> 00:16:12,100 of fruit and berries, with plenty of deer and ibex to hunt. 189 00:16:13,869 --> 00:16:18,738 But as the drought took hold, to survive they would have to adapt. 190 00:16:20,549 --> 00:16:24,542 They came up with two distinct strategies. 191 00:16:24,589 --> 00:16:28,787 One group developed this, the Harif point, 192 00:16:28,829 --> 00:16:31,104 a new, state-of-the-art arrowhead 193 00:16:31,149 --> 00:16:35,108 that allowed them to tackle a drought by hunting more efficiently. 194 00:16:35,149 --> 00:16:39,188 But a second group came up with something a little bit more subtle. 195 00:16:39,229 --> 00:16:43,142 Although you wouldn't know it, this is a sickle, 196 00:16:43,189 --> 00:16:47,546 and it offered a completely new approach to gathering food. 197 00:16:47,589 --> 00:16:51,264 This small, stone blade represented 198 00:16:51,309 --> 00:16:56,064 a decision not to chase food, but to stay put and grow it. 199 00:16:59,389 --> 00:17:02,301 The Harif point did a good job for the hunters. 200 00:17:04,589 --> 00:17:08,298 But it was the sickle that really changed history. 201 00:17:09,589 --> 00:17:13,468 In a drought, it's safer to stay close to water, 202 00:17:13,509 --> 00:17:19,027 but that decision to remain in one place meant planting crops was essential. 203 00:17:19,069 --> 00:17:21,822 If you go foraging in the forest, 204 00:17:21,869 --> 00:17:24,702 you can only collect so much food with your bare hands, 205 00:17:24,749 --> 00:17:28,458 but if you've got one of these, you can harvest fast and furious, 206 00:17:28,509 --> 00:17:32,058 and for the same amount of effort, you can collect far more food. 207 00:17:32,109 --> 00:17:34,498 With this simple tool, 208 00:17:34,549 --> 00:17:38,098 these people had begun the agricultural revolution. 209 00:17:38,149 --> 00:17:41,858 And the rest, as they say, is history. 210 00:17:45,349 --> 00:17:49,627 A lack of water and a simple but ingenious response 211 00:17:49,669 --> 00:17:52,183 led to the birth of civilisation. 212 00:17:55,869 --> 00:17:59,305 But once farming took hold, it had a profound impact 213 00:17:59,349 --> 00:18:01,260 on our relationship with water. 214 00:18:03,029 --> 00:18:06,908 No longer could we simply follow the rains. 215 00:18:06,949 --> 00:18:11,022 Now people needed regular, reliable sources of water 216 00:18:11,069 --> 00:18:13,424 to make sure their crops grew. 217 00:18:15,549 --> 00:18:19,178 So the need for water began to define 218 00:18:19,229 --> 00:18:21,902 where the first civilisations could flourish. 219 00:18:23,949 --> 00:18:27,259 That led people to the one stage of the water cycle 220 00:18:27,309 --> 00:18:30,187 that offers reliable fresh water - 221 00:18:30,229 --> 00:18:32,265 rivers. 222 00:18:33,989 --> 00:18:35,342 Across the planet, 223 00:18:35,389 --> 00:18:38,301 rivers cover a tiny proportion of the Earth's surface, 224 00:18:38,349 --> 00:18:41,978 but for the first farmers, they became magnets. 225 00:18:47,469 --> 00:18:50,461 But rivers did more than supply a steady source of water. 226 00:18:50,509 --> 00:18:54,218 They changed the very character of the civilisations 227 00:18:54,269 --> 00:18:56,578 that grew up along them, 228 00:18:56,629 --> 00:19:01,828 influencing everything from politics to social organisation. 229 00:19:04,749 --> 00:19:09,459 The power of rivers to shape history is graphically illustrated 230 00:19:09,509 --> 00:19:13,184 by perhaps the greatest of all early civilisations... 231 00:19:19,509 --> 00:19:21,784 ...Ancient Egypt. 232 00:19:23,149 --> 00:19:26,027 You might think you know the story - 233 00:19:26,069 --> 00:19:28,981 a mighty civilisation that built the pyramids 234 00:19:29,029 --> 00:19:33,102 under the autocratic rule of ruthless Pharaohs. 235 00:19:35,149 --> 00:19:38,744 But if you want to understand what really made Egypt great, 236 00:19:38,789 --> 00:19:43,146 you have to leave the pyramids and the temples behind... 237 00:19:46,029 --> 00:19:51,820 ...and come here, to a small place that hardly anyone visits. 238 00:19:51,869 --> 00:19:55,782 You know, at first glance these look like your average, everyday, 239 00:19:55,829 --> 00:19:58,343 2,OOO-year-old steps. 240 00:20:00,509 --> 00:20:04,980 But this staircase is what made Ancient Egypt tick. 241 00:20:05,029 --> 00:20:09,341 You get an idea of its true purpose by the markings on the side wall - 242 00:20:09,389 --> 00:20:12,984 these grooves were carefully carved into the marble - 243 00:20:13,029 --> 00:20:17,341 because this was a beautifully simple measuring device. 244 00:20:17,389 --> 00:20:21,223 And to see what it was measuring, you have to pop round the corner. 245 00:20:23,909 --> 00:20:25,467 Oh! 246 00:20:25,509 --> 00:20:26,908 It's all wet! 247 00:20:29,069 --> 00:20:31,663 And this is it - 248 00:20:31,709 --> 00:20:33,301 the Nile river. 249 00:20:33,349 --> 00:20:37,820 That set of steps and markings is a Nilometer. 250 00:20:37,869 --> 00:20:41,623 It measured the changing level of the river. 251 00:20:41,669 --> 00:20:45,708 Each year when it flooded, the maximum height that the waters came to 252 00:20:45,749 --> 00:20:48,627 would directly predict the yield of the crops 253 00:20:48,669 --> 00:20:51,627 and, with that, the profits that the farmers made. 254 00:20:54,869 --> 00:20:56,905 It worked because the water of the river 255 00:20:56,949 --> 00:20:59,986 carried something special within it - 256 00:21:00,029 --> 00:21:01,860 an almost invisible treasure 257 00:21:01,909 --> 00:21:06,380 that was the secret of Egypt's economic might. 258 00:21:07,949 --> 00:21:11,385 What made Egypt great is this stuff - 259 00:21:11,429 --> 00:21:13,021 silt. 260 00:21:13,069 --> 00:21:17,221 It's a rich soup of minerals, which... 261 00:21:17,269 --> 00:21:19,419 It's like an espresso. 262 00:21:19,469 --> 00:21:23,667 Tiny flecks of rock and minerals that the river picked up 263 00:21:23,709 --> 00:21:28,100 over its wandering course and swept along with the flow. 264 00:21:36,029 --> 00:21:38,543 All rivers carry some silt, 265 00:21:38,589 --> 00:21:41,661 but the Nile has the benefit of starting in Ethiopia, 266 00:21:41,709 --> 00:21:45,258 where the rock is young and volcanic. 267 00:21:46,309 --> 00:21:49,267 This forms the richest of silts. 268 00:21:49,309 --> 00:21:54,224 1 4o million tonnes of the stuff are carried by the Nile down river 269 00:21:54,269 --> 00:21:56,703 to Egypt each year. 270 00:21:56,749 --> 00:21:59,582 Every year, the seasonal flood covered the fields 271 00:21:59,629 --> 00:22:05,499 and left behind nutrient-rich silt that fertilised the crops. 272 00:22:05,549 --> 00:22:09,622 The more silt, the more food was produced. 273 00:22:09,669 --> 00:22:11,785 It was the size of the flood - 274 00:22:11,829 --> 00:22:16,857 and with it the bounty of silt - that the Nilometer was used to predict. 275 00:22:18,949 --> 00:22:24,023 So, simply by measuring the height of the Nile, the Egyptians were able 276 00:22:24,069 --> 00:22:28,585 to forecast food production and, with it, the profits of the farmers. 277 00:22:30,149 --> 00:22:34,301 Each year, they used this information to set tax levels. 278 00:22:34,349 --> 00:22:39,184 So the wealth and the might and the splendour of Ancient Egypt 279 00:22:39,229 --> 00:22:43,108 is all down to a simple twist of geographical fate. 280 00:22:43,149 --> 00:22:46,664 In fact, Ethiopia itself gets almost no benefit 281 00:22:46,709 --> 00:22:49,860 from that fertile soil washed from its highlands. 282 00:22:49,909 --> 00:22:53,618 It's even said that its greatest export is the silt 283 00:22:53,669 --> 00:22:58,618 that it sends down the Nile, silt that made the Pharaohs rich. 284 00:23:01,309 --> 00:23:04,779 But the ebb and flow of the Nile 285 00:23:04,829 --> 00:23:09,380 had more far-reaching implications for the Egyptian people than mere taxes. 286 00:23:15,349 --> 00:23:20,139 Intriguingly, it may be that where access to water is limited, 287 00:23:20,189 --> 00:23:22,305 that actually determines 288 00:23:22,349 --> 00:23:27,025 the way a society is organised and even its use of slavery. 289 00:23:30,789 --> 00:23:33,144 Where water is in short supply - 290 00:23:33,189 --> 00:23:36,101 or from a single source, as it is in Egypt - 291 00:23:36,149 --> 00:23:41,860 then you need a highly structured society to get the best out of it. 292 00:23:45,069 --> 00:23:48,459 For large-scale irrigation, you need bureaucrats to decide 293 00:23:48,509 --> 00:23:50,181 where to dig the water channels. 294 00:23:50,229 --> 00:23:53,062 You need teams of working men - slaves, really - 295 00:23:53,109 --> 00:23:55,100 to do the actual hard work of digging. 296 00:23:55,149 --> 00:23:59,461 And once the channels are in place, you need farmers with money enough 297 00:23:59,509 --> 00:24:01,579 to buy the water it's delivered. 298 00:24:01,629 --> 00:24:04,701 So right away you've got three tiers of society, 299 00:24:04,749 --> 00:24:07,582 and I haven't even mentioned the Pharaohs. 300 00:24:09,269 --> 00:24:13,501 So the rigid, hierarchical structure of Egyptian society 301 00:24:13,549 --> 00:24:17,144 wasn't just dictated by the Pharaohs. 302 00:24:17,189 --> 00:24:21,228 It also emerged because the Egyptians had only one water source - 303 00:24:21,269 --> 00:24:22,748 the Nile. 304 00:24:28,589 --> 00:24:30,466 5,ooo years ago, 305 00:24:30,509 --> 00:24:34,343 it wasn't just the Ancient Egyptians who noticed the value of rivers. 306 00:24:36,229 --> 00:24:41,383 Other great civilisations were also forming along the banks of rivers. 307 00:24:42,949 --> 00:24:44,780 In Mesopotamia, 308 00:24:44,829 --> 00:24:50,028 the Sumerian civilisation flourished between the Tigris and the Euphrates. 309 00:24:51,949 --> 00:24:57,262 Further east, the Harappan civilisation formed by the Indus. 310 00:24:59,149 --> 00:25:04,348 And early Chinese civilisations were emerging along the Yellow River. 311 00:25:08,629 --> 00:25:12,941 But not all early farmers were content to settle by rivers. 312 00:25:12,989 --> 00:25:15,901 Others learned to exploit new sources of water, 313 00:25:15,949 --> 00:25:18,179 in the unlikeliest places. 314 00:25:20,309 --> 00:25:23,267 Like the Sahara Desert, in Libya. 315 00:25:32,589 --> 00:25:36,264 These are the remains of the ancient city of Garama, 316 00:25:36,309 --> 00:25:41,702 which about 2,5oo years ago was the centre of a powerful empire. 317 00:25:41,749 --> 00:25:45,458 Today, it's a bit of a maze, but from up here 318 00:25:45,509 --> 00:25:49,707 you can see the shapes of the buildings, the way the streets interconnect. 319 00:25:55,629 --> 00:25:59,622 You get a real sense of how this place must have worked in its prime. 320 00:26:08,989 --> 00:26:11,708 This was the home of the Garamantians... 321 00:26:13,269 --> 00:26:16,420 ...which, for me, are a rather forgotten people. 322 00:26:16,469 --> 00:26:20,462 They've been eclipsed in the history books by their showy contemporaries, 323 00:26:20,509 --> 00:26:22,306 the Greeks and the Romans. 324 00:26:22,349 --> 00:26:28,140 The Garamantians dominated the Sahara Desert for almost 2,OOO years. 325 00:26:28,189 --> 00:26:32,819 They were the society that first brought civilisation to the desert. 326 00:26:36,269 --> 00:26:40,740 Far from just scraping by in this harsh landscape, 327 00:26:40,789 --> 00:26:43,428 the Garamantes were flourishing. 328 00:26:45,069 --> 00:26:48,618 They grew crops such as cereals and grapes. 329 00:26:48,669 --> 00:26:50,978 They kept horses and pigs. 330 00:26:51,029 --> 00:26:54,339 Clearly, they needed large amounts of water. 331 00:26:57,029 --> 00:27:00,658 So where did they find it, here in the middle of the desert? 332 00:27:04,509 --> 00:27:09,185 Now, this is the key to the Garamantians' incredible success. 333 00:27:09,229 --> 00:27:13,063 It's vertical holes that are sunk deep into the ground... 334 00:27:14,509 --> 00:27:20,186 ...4O to 5O metres - that's about 1 5O feet. 335 00:27:20,229 --> 00:27:22,106 And the purpose of them was pretty simple - 336 00:27:22,149 --> 00:27:24,617 it was to bring water up from below ground. 337 00:27:24,669 --> 00:27:28,344 In this environment, it must have seemed like it was almost magic. 338 00:27:28,389 --> 00:27:32,701 In fact, the Garamantians had discovered groundwater. 339 00:27:34,589 --> 00:27:38,582 Beneath the surface of the Sahara is a surprising part 340 00:27:38,629 --> 00:27:40,540 of the great water cycle - 341 00:27:40,589 --> 00:27:43,661 a massive store of groundwater. 342 00:27:47,429 --> 00:27:50,501 This is water that has seeped into the ground 343 00:27:50,549 --> 00:27:54,383 and has collected in porous layers of rock. 344 00:27:54,429 --> 00:27:56,659 The water came from the period 345 00:27:56,709 --> 00:28:01,942 thousands of years before, when the Sahara was lush and wet. 346 00:28:03,509 --> 00:28:08,378 Some of that water percolated into the rocks below and remained there, 347 00:28:08,429 --> 00:28:11,387 despite the dramatic drying above... 348 00:28:12,989 --> 00:28:17,062 ...until the Garamantes found it. 349 00:28:17,109 --> 00:28:19,987 You kind of dig them down until you hit the water table 350 00:28:20,029 --> 00:28:22,338 and then you just keep doing the same thing. 351 00:28:22,389 --> 00:28:26,985 There's one after another, after another, all in a whole line. 352 00:28:28,149 --> 00:28:32,267 But these holes aren't wells - they're maintenance shafts. 353 00:28:32,309 --> 00:28:36,302 They reach down to tunnels which carried the water. 354 00:28:36,349 --> 00:28:40,262 The point is, right up there at the end is where the water source is, 355 00:28:40,309 --> 00:28:44,541 so the water flows naturally from the escarpment up there, underground, 356 00:28:44,589 --> 00:28:47,387 down to the kind of oasis over there. 357 00:28:47,429 --> 00:28:50,068 Now, that's where the Garamantians' city was. 358 00:28:50,109 --> 00:28:53,465 What they could have done is they could have dug wells down 359 00:28:53,509 --> 00:28:57,946 and lifted the water out, but that's a lot of work for very little return. 360 00:28:57,989 --> 00:29:01,186 Much better to use gravity to channel the water 361 00:29:01,229 --> 00:29:04,187 in an underground tunnel straight to where they need it. 362 00:29:05,749 --> 00:29:09,378 That was the Garamantians' real ingenuity. 363 00:29:13,349 --> 00:29:17,422 The Garamantes had managed to tap the same water 364 00:29:17,469 --> 00:29:22,145 that the early Saharans had enjoyed thousands of years earlier. 365 00:29:22,189 --> 00:29:25,625 By mining groundwater, the Garamantians managed 366 00:29:25,669 --> 00:29:30,868 to turn the clock back on the Sahara - they made the desert bloom again. 367 00:29:33,309 --> 00:29:36,619 But the human struggle to pin down water 368 00:29:36,669 --> 00:29:39,467 is forever balanced on a knife edge. 369 00:29:39,549 --> 00:29:43,224 Get that balance wrong and you pay the price. 370 00:29:44,269 --> 00:29:50,902 For all their ingenuity, the Garamantes over-exploited their groundwater. 371 00:29:50,949 --> 00:29:56,103 Eventually it ran out, and so did their civilisation. 372 00:29:57,469 --> 00:30:00,905 Now all that remains are the bats. 373 00:30:00,949 --> 00:30:02,860 (SQUEAKING AND FLUTTERING) 374 00:30:07,069 --> 00:30:12,189 Today, modern Libyans have tapped into this same groundwater supply, 375 00:30:12,229 --> 00:30:16,939 by using pumps to reach deeper than the Garamantes could. 376 00:30:16,989 --> 00:30:22,507 But just like their ancient predecessors, they're exploiting a finite resource. 377 00:30:22,549 --> 00:30:26,747 At most, it will last only another 5o years. 378 00:30:29,029 --> 00:30:33,580 But water in this most inaccessible stage of the water cycle 379 00:30:33,629 --> 00:30:35,859 is found in many other places. 380 00:30:37,429 --> 00:30:41,820 It's at its most spectacular in Tallahassee, in Florida. 381 00:30:43,909 --> 00:30:49,188 Here, divers are just beginning to explore a mysterious series of caves 382 00:30:49,229 --> 00:30:55,259 called a karst system, carved out by groundwater over millions of years. 383 00:30:58,109 --> 00:31:02,546 This is one of the planet's least known frontiers. 384 00:31:03,589 --> 00:31:06,262 When they began, these divers had no idea 385 00:31:06,309 --> 00:31:08,265 of the extent of the cave network. 386 00:31:11,669 --> 00:31:16,060 To explore these caves, they've made the longest dives in history, 387 00:31:16,109 --> 00:31:19,863 travelling more than ten kilometres from the cave entrance. 388 00:31:22,669 --> 00:31:27,379 They're sometimes underwater for 24 hours at a time. 389 00:31:32,189 --> 00:31:34,419 Their efforts have revealed 390 00:31:34,469 --> 00:31:38,178 one of the world's largest underwater cave systems. 391 00:31:39,749 --> 00:31:44,220 It's part of a huge store of groundwater, of varying depths, 392 00:31:44,269 --> 00:31:49,707 that underlies all of Florida and reaches into neighbouring states. 393 00:31:49,749 --> 00:31:52,217 And it's not just the USA. 394 00:31:52,269 --> 00:31:56,945 There's groundwater in the most unexpected places. 395 00:31:56,989 --> 00:32:01,858 More than 3o% of all the fresh water on Earth is under our feet. 396 00:32:04,069 --> 00:32:10,907 Looked at this way, our apparently solid planet is more like a sponge. 397 00:32:18,189 --> 00:32:20,100 In our early history, 398 00:32:20,149 --> 00:32:25,621 the need for reliable supplies of water led us to rivers and groundwater. 399 00:32:28,789 --> 00:32:33,419 But as humans spread across the planet, they learned to exploit 400 00:32:33,469 --> 00:32:37,144 the vagaries of the water cycle in many different ways. 401 00:32:41,269 --> 00:32:44,022 The key was adaptation. 402 00:32:45,589 --> 00:32:47,580 (THUNDER RUMBLES) 403 00:32:48,589 --> 00:32:50,739 Take rain. 404 00:32:55,309 --> 00:32:59,666 A familiar occurrence in many parts of the world. 405 00:32:59,709 --> 00:33:03,224 But this is rain at its most extreme - 406 00:33:03,269 --> 00:33:05,066 the monsoon. 407 00:33:14,309 --> 00:33:18,268 The significance of the monsoon isn't the human discomfort 408 00:33:18,309 --> 00:33:22,621 but how the people here have learned to live with it. 409 00:33:23,709 --> 00:33:26,826 I'm travelling to the very epicentre of the monsoon, 410 00:33:26,869 --> 00:33:29,303 a place called Cherrapunjee, 411 00:33:29,349 --> 00:33:34,139 which holds the world record for the highest rainfall in a single year. 412 00:33:43,749 --> 00:33:46,138 (THUNDER RUMBLES) 413 00:33:46,189 --> 00:33:49,386 I thought I knew rain. 414 00:33:49,429 --> 00:33:52,580 If you're from the west of Scotland, you've met rain before, 415 00:33:52,629 --> 00:33:54,665 but this is different, it's different rain. 416 00:33:54,709 --> 00:33:57,507 It's hard to explain. It's the sheer intensity of it - 417 00:33:57,549 --> 00:33:59,141 it just comes barrelling down. 418 00:33:59,189 --> 00:34:02,101 But also, the raindrops are massive. 419 00:34:02,149 --> 00:34:05,858 You feel as if you could fill an egg cup with them, which means that, 420 00:34:05,909 --> 00:34:07,661 within minutes, you're just soaked. 421 00:34:07,709 --> 00:34:10,428 It's pointless with a hood and all the rest of it - I'm soaked. 422 00:34:10,469 --> 00:34:13,029 What I really need is a brolly, like this chap. 423 00:34:14,589 --> 00:34:16,227 Very wet! 424 00:34:17,469 --> 00:34:18,584 Wet. 425 00:34:18,629 --> 00:34:20,620 Just watch it, it's very slidy. 426 00:34:24,149 --> 00:34:28,028 Back in west Scotland, where I'm from, the average annual rainfall 427 00:34:28,069 --> 00:34:32,745 is nearly a metre, and that might horrify a Californian, 428 00:34:32,789 --> 00:34:36,862 but here in Cherrapunjee, the annual average rainfall 429 00:34:36,909 --> 00:34:42,302 is more than ten times that - between 1 1 and 1 2 metres. 430 00:34:42,349 --> 00:34:45,421 That's nearly the height of a four-storey building. 431 00:34:50,749 --> 00:34:56,301 Streams turn to rivers, and rivers turn to torrents. 432 00:35:01,629 --> 00:35:05,747 When you live with so much water, you have to adapt... 433 00:35:05,789 --> 00:35:08,019 just to get around. 434 00:35:08,069 --> 00:35:12,028 And that's exactly what the local Khasi people have done. 435 00:35:21,669 --> 00:35:23,899 Look at this! 436 00:35:23,949 --> 00:35:27,498 Isn't this fantastic? Look at it! 437 00:35:27,549 --> 00:35:33,465 It's a living bridge - look, you can see all these roots coming down. 438 00:35:33,509 --> 00:35:35,818 The texture of them is beautiful. 439 00:35:42,269 --> 00:35:46,899 I mean, this entire structure is built of growing rubber tree. 440 00:35:52,029 --> 00:35:53,826 It's just mad when you follow it! 441 00:35:56,109 --> 00:35:59,784 You can see that this is the perfect union of the tree and the villagers. 442 00:35:59,829 --> 00:36:02,218 The locals have kind of trained the roots, 443 00:36:02,269 --> 00:36:05,500 kind of guided them through, knitted them together. 444 00:36:08,709 --> 00:36:11,781 What they've done here is they've grabbed some rootlets like this 445 00:36:11,829 --> 00:36:14,297 and taken it round. And look, here it is... 446 00:36:14,349 --> 00:36:17,625 this set of rootlets here. That's incredibly strong. 447 00:36:17,669 --> 00:36:19,387 It's an anchor for the bridge. 448 00:36:21,669 --> 00:36:26,379 Ordinary bridges would rot under the relentless drenching of the monsoon. 449 00:36:26,429 --> 00:36:31,708 What's clever about these root bridges is they get stronger as they get older. 450 00:36:31,749 --> 00:36:35,947 So wide! I mean, a whole village could get through here. 451 00:36:37,349 --> 00:36:39,146 (THUNDER RUMBLES) 452 00:36:46,229 --> 00:36:50,427 Surprisingly, the intensity of the monsoon rain is all down 453 00:36:50,469 --> 00:36:52,505 to a basic property of water. 454 00:36:57,869 --> 00:37:02,624 Compared to other substances, water takes a lot of energy to heat up. 455 00:37:06,189 --> 00:37:09,420 So the land and the ocean react very differently 456 00:37:09,469 --> 00:37:12,506 to the rising temperatures of early summer. 457 00:37:15,509 --> 00:37:19,548 During these months, India's land surface heats up much more 458 00:37:19,589 --> 00:37:21,864 than the surrounding Indian Ocean. 459 00:37:23,749 --> 00:37:27,458 The high temperature reduces the density of the air, 460 00:37:27,509 --> 00:37:30,069 creating low pressure. 461 00:37:30,109 --> 00:37:34,068 That sucks moist ocean air onto the land, 462 00:37:34,109 --> 00:37:36,577 which brings rain. 463 00:37:40,509 --> 00:37:43,706 It's because the whole system is driven by the sun's heat 464 00:37:43,749 --> 00:37:45,865 that the rains come in the summer. 465 00:37:48,029 --> 00:37:50,907 But it also means that the monsoon 466 00:37:50,949 --> 00:37:54,339 only lasts for three months of the year. 467 00:37:54,389 --> 00:37:58,507 For the rest of the time, there's virtually no rain. 468 00:38:00,869 --> 00:38:02,700 (TRAIN HOOTER BLARES) 469 00:38:06,709 --> 00:38:09,177 The people of India have adapted, 470 00:38:09,229 --> 00:38:12,585 as much as they can, to these extremes of the monsoon. 471 00:38:13,829 --> 00:38:15,421 I think it's this way. 472 00:38:15,469 --> 00:38:18,347 It's great, you have to use your elbows in here. 473 00:38:24,829 --> 00:38:28,299 But outsiders are not always so sensitive to its rhythms. 474 00:38:33,229 --> 00:38:37,745 Here in India, the changing strength of the monsoon year on year 475 00:38:37,789 --> 00:38:42,305 had really tremendous impacts on the country's political fortunes. 476 00:38:42,349 --> 00:38:45,978 That's especially true of its recent colonial past, 477 00:38:46,029 --> 00:38:47,781 the story of which was played out 478 00:38:47,829 --> 00:38:51,538 against a backdrop of water abundance and scarcity. 479 00:38:51,589 --> 00:38:54,706 Clearly there are lots of reasons to explain the fate 480 00:38:54,749 --> 00:38:56,785 of British colonial rule in India, 481 00:38:56,829 --> 00:39:01,300 but one of the least explored and most intriguing is water. 482 00:39:04,869 --> 00:39:07,781 In the 1 9th century, the failure of the British 483 00:39:07,829 --> 00:39:12,345 to manage India's water supply had significant consequences... 484 00:39:12,389 --> 00:39:14,619 for them and for the Indian people. 485 00:39:23,349 --> 00:39:27,137 Perhaps it was naivety, perhaps it was because they were outsiders, 486 00:39:27,189 --> 00:39:31,307 perhaps it was their inability to cope with extreme weather, 487 00:39:31,349 --> 00:39:35,103 but the British never really got to grips with the monsoon. 488 00:39:40,109 --> 00:39:43,260 For thousands of years, people here have been developing ways 489 00:39:43,309 --> 00:39:45,140 to deal with the monsoon. 490 00:39:45,189 --> 00:39:49,228 And this was one of the most important - it's a huge open well 491 00:39:49,269 --> 00:39:53,182 that was dug down deep enough to reach groundwater. 492 00:39:53,229 --> 00:39:58,462 When the rains came, the water was filtered through the surrounding ground 493 00:39:58,509 --> 00:40:02,218 and held in the well like a gigantic bucket. 494 00:40:02,269 --> 00:40:05,022 But these stepwells, as they were known, 495 00:40:05,069 --> 00:40:07,378 were more than water collectors. 496 00:40:07,429 --> 00:40:11,547 The genius of this design was it turned the mundane need for water 497 00:40:11,589 --> 00:40:13,784 into a social ritual. 498 00:40:13,829 --> 00:40:18,459 People didn't just come here to dip for water - they gossiped, 499 00:40:18,509 --> 00:40:20,898 they bathed, they even worshipped. 500 00:40:24,829 --> 00:40:28,947 Over 3,ooo stepwells were built, up until the 1 9th century. 501 00:40:29,989 --> 00:40:33,902 For millions, they were the main source of water. 502 00:40:38,349 --> 00:40:41,307 Despite the fact that structures like this helped the Indian people 503 00:40:41,349 --> 00:40:44,147 survive droughts, the British didn't like it. 504 00:40:44,189 --> 00:40:47,147 They were concerned that people bathing in the same water they drank from 505 00:40:47,189 --> 00:40:49,225 was bad news. 506 00:40:49,269 --> 00:40:52,306 So on health grounds, they shut them down. 507 00:40:52,349 --> 00:40:54,340 I mean, they may have had a point, 508 00:40:54,389 --> 00:40:57,984 and they solved that issue by bringing in piped water, 509 00:40:58,029 --> 00:41:00,827 but at the same time, they imported another problem 510 00:41:00,869 --> 00:41:02,939 that was much, much worse. 511 00:41:05,029 --> 00:41:06,587 It's a little-known fact, 512 00:41:06,629 --> 00:41:10,747 but the British built canals on a colossal scale across India, 513 00:41:10,789 --> 00:41:13,428 more than 57,ooo kilometres of them - 514 00:41:13,469 --> 00:41:17,382 perhaps their biggest engineering achievement anywhere. 515 00:41:20,469 --> 00:41:24,178 Yet the British didn't realise that, even more than stepwells, 516 00:41:24,229 --> 00:41:28,507 these huge bodies of standing water were a health hazard - 517 00:41:28,549 --> 00:41:33,225 the perfect environment for malaria to breed and spread. 518 00:41:38,349 --> 00:41:42,945 Given the lack of sensitivity the British showed to the Indian climate, 519 00:41:42,989 --> 00:41:47,346 it's perhaps ironic that the monsoon played a significant role 520 00:41:47,389 --> 00:41:50,267 in undermining British rule in India. 521 00:41:57,629 --> 00:42:01,622 At the end of the 1 9th century, the monsoon rains failed. 522 00:42:07,109 --> 00:42:10,385 For a decade, there were repeated droughts. 523 00:42:10,429 --> 00:42:13,978 Crops were ruined, and there were terrible famines. 524 00:42:16,069 --> 00:42:19,266 But the British failed to respond effectively - 525 00:42:19,309 --> 00:42:23,985 in fact, they even continued to export rice. 526 00:42:24,029 --> 00:42:28,147 This indifference to the rhythms of the monsoon fuelled popular anger 527 00:42:28,189 --> 00:42:33,388 against colonial rule, and the independence movement grew rapidly. 528 00:42:42,469 --> 00:42:44,937 Today, the stepwells are being repaired. 529 00:42:47,789 --> 00:42:50,508 Pumps accessing groundwater are used to protect 530 00:42:50,549 --> 00:42:52,619 against the unreliable monsoon. 531 00:42:54,629 --> 00:42:59,828 And that's made India the largest user of groundwater in the world. 532 00:43:08,789 --> 00:43:12,464 Adapting to the water cycle has meant the difference between success 533 00:43:12,509 --> 00:43:15,148 and failure for many civilisations. 534 00:43:20,389 --> 00:43:24,826 But there was another strategy that also brought success... 535 00:43:25,829 --> 00:43:29,742 ...and that was to take control of the water cycle. 536 00:43:35,429 --> 00:43:39,707 There was one early civilisation above all others that took control 537 00:43:39,749 --> 00:43:43,298 of the planet's most dramatically changing source of water. 538 00:43:44,949 --> 00:43:47,782 They mastered the monsoon. 539 00:43:52,469 --> 00:43:54,380 They were the Khmers, 540 00:43:54,429 --> 00:43:57,227 and from the 9th century, they dominated the area 541 00:43:57,269 --> 00:44:00,466 we now know as Cambodia. 542 00:44:00,509 --> 00:44:03,706 And this was their greatest achievement... 543 00:44:03,749 --> 00:44:07,867 the legendary temple complex of Angkor. 544 00:44:14,789 --> 00:44:17,906 You get a real sense of the age of this place here, 545 00:44:17,949 --> 00:44:20,543 cos this was built over 1,2OO years ago. 546 00:44:22,229 --> 00:44:25,619 In a few places, like here, you can see it's showing the age. 547 00:44:25,669 --> 00:44:28,945 Look, the faces have all gone, 548 00:44:28,989 --> 00:44:34,063 but, look at this, that looks as if it could have been carved just yesterday. 549 00:44:37,669 --> 00:44:39,705 (THUNDER CRASHES) 550 00:44:43,229 --> 00:44:45,584 Angkor was built to honour the Hindu gods 551 00:44:45,629 --> 00:44:49,588 and it symbolised the extraordinary success of the Khmers. 552 00:44:54,549 --> 00:44:57,507 In a way, this place is a monument to something else - 553 00:44:57,549 --> 00:45:02,225 the Khmers' ability to harness the power of the monsoon. 554 00:45:13,109 --> 00:45:15,464 The Khmers were first drawn to this region 555 00:45:15,509 --> 00:45:19,297 by the Tonle Sap lake and the river that feeds it. 556 00:45:22,989 --> 00:45:27,267 Today, it's home to a floating, permanent community, 557 00:45:27,309 --> 00:45:29,504 replete with all the necessary amenities. 558 00:45:37,389 --> 00:45:39,539 All life here is lived on the river - 559 00:45:39,589 --> 00:45:45,221 the whole village, houses, shops, churches, schools, everything. 560 00:45:49,069 --> 00:45:51,537 A hardware store! 561 00:45:55,789 --> 00:45:59,145 Everybody's watching telly. They're all watching soap operas, 562 00:45:59,189 --> 00:46:01,066 orjust chilling out. 563 00:46:02,269 --> 00:46:05,466 People settle here today for the same reason 564 00:46:05,509 --> 00:46:08,865 the Khmers did over 1,ooo years ago - 565 00:46:08,909 --> 00:46:13,824 the unusual behaviour of the lake around monsoon time. 566 00:46:13,869 --> 00:46:18,067 Each year when the monsoon rains fall, the land around here 567 00:46:18,109 --> 00:46:23,820 just can't drain fast enough, and this lake, Tonle Sap, swells enormously. 568 00:46:23,869 --> 00:46:28,579 It more than trebles in size, becoming, forjust a few months, 569 00:46:28,629 --> 00:46:32,099 the largest freshwater lake in Southeast Asia. 570 00:46:39,709 --> 00:46:44,260 And every year, the water brings with it a spectacular bounty. 571 00:46:49,869 --> 00:46:54,989 Fish! Loads of them, nibbling away at your toes in this murky water. 572 00:46:58,149 --> 00:47:01,107 So many, that when it floods, the Tonle Sap lake 573 00:47:01,149 --> 00:47:04,903 becomes the richest source of freshwater fish in the world. 574 00:47:08,229 --> 00:47:11,460 Back in the 9th century, the Khmers realised 575 00:47:11,509 --> 00:47:16,583 that this annual influx of fish and water offered a glittering opportunity. 576 00:47:20,509 --> 00:47:24,741 They set about building a fishing industry here, and with the profits, 577 00:47:24,789 --> 00:47:27,144 they built the temples of Angkor. 578 00:47:30,469 --> 00:47:35,020 But as it grew, the Khmer kingdom faced a stumbling block. 579 00:47:36,269 --> 00:47:41,707 When the monsoon finished each year, the fish and water would vanish. 580 00:47:41,749 --> 00:47:46,220 So each year, the inhabitants were plunged into drought and hunger. 581 00:47:46,269 --> 00:47:49,944 The Khmer rose to the challenge magnificently. 582 00:47:49,989 --> 00:47:54,267 They decided that rather than be at the whim of the monsoon, 583 00:47:54,309 --> 00:47:56,664 they would make it work for them. 584 00:48:12,309 --> 00:48:14,106 This is part of a vast network 585 00:48:14,149 --> 00:48:18,028 of irrigation tunnels that crisscross the whole of Angkor. 586 00:48:18,069 --> 00:48:21,141 When the Khmer started digging these in the 9th century, 587 00:48:21,189 --> 00:48:23,464 people had seen nothing like them. 588 00:48:23,509 --> 00:48:26,785 This was plumbing on a grand scale. 589 00:48:36,949 --> 00:48:39,907 From the air, it's still visible today. 590 00:48:42,349 --> 00:48:46,820 Over 1,ooo years ago, the Khmers managed to divert a river 591 00:48:46,869 --> 00:48:48,905 by 8o kilometres. 592 00:48:50,709 --> 00:48:52,267 They built canals 593 00:48:52,309 --> 00:48:57,337 that extended over an area of 1,ooo square kilometres 594 00:48:57,389 --> 00:48:58,947 and dug reservoirs 595 00:48:58,989 --> 00:49:03,983 that could hold up to 6oo million cubic metres of monsoon water. 596 00:49:06,509 --> 00:49:11,947 With this system, the Khmers seized control of the planet's water cycle. 597 00:49:11,989 --> 00:49:15,902 They turned the seasonal rainfall of the monsoon into a reliable, 598 00:49:15,949 --> 00:49:18,827 all-year-round water supply. 599 00:49:20,869 --> 00:49:25,147 It was an enormous achievement, enabling Angkor at its peak 600 00:49:25,189 --> 00:49:28,898 to support a population in excess of one million. 601 00:49:33,789 --> 00:49:36,940 Thanks to their control of water, 602 00:49:36,989 --> 00:49:41,141 the Khmers had built the largest pre-industrial city in the world. 603 00:49:52,149 --> 00:49:55,141 The Khmer hung on until the 1 5th century, 604 00:49:55,189 --> 00:49:59,626 which was when the kingdom of Angkor finally went to the wall. 605 00:49:59,669 --> 00:50:02,058 They were victims of their own success. 606 00:50:02,109 --> 00:50:04,384 Their population went through the roof, 607 00:50:04,429 --> 00:50:08,217 and they simply outstripped their resources, including - 608 00:50:08,269 --> 00:50:11,659 despite all that incredible engineering - 609 00:50:11,709 --> 00:50:13,904 including the water supply. 610 00:50:13,949 --> 00:50:15,667 I guess that there are limits 611 00:50:15,709 --> 00:50:18,667 to what even the mighty monsoon can sustain. 612 00:50:27,189 --> 00:50:31,023 Today, we control water on a massive scale. 613 00:50:34,269 --> 00:50:41,107 The world's reservoirs now hold over 1 o,ooo cubic kilometres of water. 614 00:50:41,149 --> 00:50:46,667 That's five times as much water as in all the rivers on Earth. 615 00:50:48,789 --> 00:50:53,101 And because most of it is pooled in the more populated northern hemisphere, 616 00:50:53,149 --> 00:50:57,347 away from the equator, the extra weight has slightly changed how the Earth 617 00:50:57,389 --> 00:50:59,061 spins on its axis. 618 00:50:59,109 --> 00:51:01,828 It's caused the Earth's rotation to speed up, 619 00:51:01,869 --> 00:51:07,148 shortening the day by 8 millionths of a second in the last 4o years. 620 00:51:15,789 --> 00:51:19,543 Today, we take our control of water for granted. 621 00:51:19,589 --> 00:51:23,582 Modern civilisation couldn't exist without it. 622 00:51:24,989 --> 00:51:29,107 But there's still only a finite amount of water to go around. 623 00:51:29,149 --> 00:51:32,107 In many parts of the world, 624 00:51:32,149 --> 00:51:37,587 scarcity has led to a bitter struggle for control over the available supply. 625 00:51:37,629 --> 00:51:41,258 And that's true in even the wealthiest countries. 626 00:51:42,869 --> 00:51:48,068 Today, Los Angeles is a city with every luxury and convenience. 627 00:51:53,509 --> 00:51:56,148 Yet not so long ago, at the turn of the last century, 628 00:51:56,189 --> 00:51:59,340 Los Angeles was struggling. 629 00:52:00,469 --> 00:52:05,862 LA 's problem was its location, hemmed in on three sides by desert 630 00:52:05,909 --> 00:52:08,469 and on the fourth by ocean. 631 00:52:08,509 --> 00:52:12,263 So it lacked the most basic requirement for city life - 632 00:52:12,309 --> 00:52:14,743 a reliable water supply. 633 00:52:17,469 --> 00:52:21,508 So it came up with a plan to get the water it so needed. 634 00:52:28,269 --> 00:52:31,784 4oo kilometres to the north of the growing city, 635 00:52:31,829 --> 00:52:34,821 nestled within the Sierra Nevada mountain range, 636 00:52:34,869 --> 00:52:37,702 was a place called Owens Valley. 637 00:52:38,869 --> 00:52:44,068 It was a verdant place, where people were settling and building farms. 638 00:52:44,109 --> 00:52:47,306 At the heart of it was plentiful water - 639 00:52:47,349 --> 00:52:50,307 a wide river feeding a huge lake. 640 00:52:55,189 --> 00:52:59,705 This valley must have seemed like the answer to Los Angeles' prayers. 641 00:52:59,749 --> 00:53:02,547 There was enough water here to easily supply 642 00:53:02,589 --> 00:53:04,500 over one million people. 643 00:53:04,549 --> 00:53:06,426 There was only one problem... 644 00:53:06,469 --> 00:53:08,141 it didn't belong to them. 645 00:53:08,189 --> 00:53:12,148 It belonged to the farmers of Owens Valley. 646 00:53:12,189 --> 00:53:15,067 It would have to be taken by stealth. 647 00:53:25,629 --> 00:53:28,063 It wasn't long before men appeared in the valley, 648 00:53:28,109 --> 00:53:30,179 masquerading as investors. 649 00:53:32,069 --> 00:53:36,984 They offered to buy up farmland at seemingly irresistible prices, 650 00:53:37,029 --> 00:53:39,702 just to get the water rights that went with it. 651 00:53:41,269 --> 00:53:45,182 It wasn't technically illegal, but it was certainly shady. 652 00:53:46,269 --> 00:53:48,499 And it worked. 653 00:53:48,549 --> 00:53:52,178 In 1 91 3, after six years of construction, 654 00:53:52,229 --> 00:53:54,026 an aqueduct was opened. 655 00:53:54,069 --> 00:53:55,548 And this is it. 656 00:54:08,749 --> 00:54:11,741 In a way, this aqueduct was a triumph, 657 00:54:11,789 --> 00:54:14,462 certainly as far as Los Angeles was concerned. 658 00:54:14,509 --> 00:54:17,342 It allowed millions of people 2OO miles down there 659 00:54:17,389 --> 00:54:20,506 to live in a growing and vibrant city. 660 00:54:20,549 --> 00:54:23,427 But that's not how people here saw it. 661 00:54:25,109 --> 00:54:29,068 The Owens Valley farmers didn't give up without a struggle. 662 00:54:31,429 --> 00:54:33,659 A kind of loose resistance movement started, 663 00:54:33,709 --> 00:54:37,384 and they would take over places like this and open the sluice gates, 664 00:54:37,429 --> 00:54:40,501 allowing the water to pour back down into Owens Valley. 665 00:54:40,549 --> 00:54:44,588 And regularly they'd dynamite the aqueduct. 666 00:54:47,109 --> 00:54:48,622 But the city rebuilt it, 667 00:54:48,669 --> 00:54:51,741 and a game of cat and mouse continued 668 00:54:51,789 --> 00:54:54,622 for three more dynamite-filled years. 669 00:54:54,669 --> 00:54:59,504 Eventually, the police clamped down with a ''shoot to kill'' policy, 670 00:54:59,549 --> 00:55:01,380 and the rebellion fizzled out. 671 00:55:01,429 --> 00:55:04,102 The city had won. 672 00:55:08,909 --> 00:55:13,903 Today, the Los Angeles Aqueduct is just part of a giant network 673 00:55:13,949 --> 00:55:18,465 of pipes and aqueducts all serving one of the world's great cities. 674 00:55:37,229 --> 00:55:40,619 But, back in Owens Valley, the lake has all but vanished, 675 00:55:40,669 --> 00:55:43,581 and the river is barely a trickle. 676 00:55:45,829 --> 00:55:50,220 The story of Owens Valley is not an isolated case. 677 00:55:50,269 --> 00:55:54,785 Today, there are conflicts over water taking place all around the world. 678 00:55:59,589 --> 00:56:02,740 Israel, the Palestinians, Syria and Jordan 679 00:56:02,789 --> 00:56:05,349 dispute access to the River Jordan. 680 00:56:07,509 --> 00:56:12,299 Egypt, Sudan and Ethiopia quarrel over the waters of the Nile. 681 00:56:16,069 --> 00:56:18,583 On the Indus river, 682 00:56:18,629 --> 00:56:23,419 India and Pakistan are in conflict over dams built on the river's tributaries. 683 00:56:23,469 --> 00:56:26,541 And these are only some of the more well-known examples. 684 00:56:31,109 --> 00:56:34,306 1 o,ooo years ago, we lived at the whim 685 00:56:34,349 --> 00:56:37,182 of the unpredictable water cycle. 686 00:56:39,709 --> 00:56:43,304 Since then, we have harnessed the power of rivers 687 00:56:43,349 --> 00:56:45,624 to advance our civilisations. 688 00:56:49,669 --> 00:56:52,467 We have extracted groundwater from the depths 689 00:56:52,509 --> 00:56:54,101 of the most unlikely places. 690 00:56:56,509 --> 00:57:01,537 And we have learned to redirect and store water on a massive scale. 691 00:57:07,989 --> 00:57:12,460 Today, we have unprecedented power over the planet's water. 692 00:57:14,029 --> 00:57:16,338 But one thing hasn't changed - 693 00:57:16,389 --> 00:57:20,905 there's still only a finite amount of water on Earth. 694 00:57:28,189 --> 00:57:29,668 It seems to me 695 00:57:29,709 --> 00:57:33,418 that water is the Achilles heel of our modern civilisation. 696 00:57:33,469 --> 00:57:35,266 It's the one resource, 697 00:57:35,309 --> 00:57:36,537 more than any other, 698 00:57:36,589 --> 00:57:39,342 with the potential to limit our ambitions. 699 00:57:41,349 --> 00:57:45,627 The fundamental limits of the water cycle are still there. 700 00:57:45,669 --> 00:57:50,299 But the lesson of history is that the most successful civilisations 701 00:57:50,349 --> 00:57:52,783 learn to adapt to those limits. 702 00:57:54,469 --> 00:57:57,381 So the problem is more with us. 703 00:57:57,429 --> 00:58:02,549 Now, that prospect may find you gloomy or, like me, more optimistic. 704 00:58:02,589 --> 00:58:07,344 But either way, at least the future's in our hands. 705 00:58:10,149 --> 00:58:13,300 Next time, the contradictory role of the deep Earth. 706 00:58:15,309 --> 00:58:18,984 It drove great technological breakthroughs, 707 00:58:19,029 --> 00:58:21,702 but its gifts... 708 00:58:21,749 --> 00:58:23,387 came at a price.